In industrialized nations, colorectal cancer is the second leading cause of deaths from malignancy. In the United States, almost 150,000 people are found to have colon cancer annually and it causes approximately 60,000 deaths annually. Only lung cancer causes more deaths. Colon cancers are preventable because they usually begin as benign polyps which grow slowly for five to ten years before becoming cancerous. If these polyps are detected and removed, the risk of developing colon cancer is greatly reduced.
Unfortunately, widespread colorectal screening and preventive efforts are hampered by several practical impediments, including limited resources, methodologic inadequacies, and poor patient acceptance leading to poor compliance. In addition, a fecal occult blood test (FOBT) fails to detect the majority of cancers and pre cancerous polyps. Since sigmoidoscopy only examines a portion of the colon, it also misses many polyps. The accuracy of barium enema varies among centers and is therefore not always reliable.
Therefore, there is a need for a new test which can be used to screen for pre cancerous colon polyps. Like all screening tests, this new test must be relatively inexpensive, minimally invasive, and highly specific.
A technique using helical computed tomography (CT) to create computer simulated intraluminal flights through the colon was proposed as a novel approach for detecting colorectal neoplasms by Vining D J, Shifrin R Y, Grishaw E K, Liu K, Gelfand D W, Virtual colonoscopy (Abst), Radiology Scientific Prgm 1994; 193(P):446. This technique was first described by Vining et al. in an earlier abstract by Vining D J, Gelfand DW, Noninvasive colonoscopy using helical CT scanning, 3D reconstruction, and virtual reality (Abst), SGR Scientific Program, 1994. This technique, referred to as "virtual colonoscopy", requires a cleansed colon insufflated with air, a helical CT scan of approximately 30 seconds, and specialized three-dimensional (3D) imaging software to extract and display the mucosal surface. The resulting endoluminal images generated by the CT scan are displayed to a medical practitioner for diagnostic purposes.
The technique of reformatting 2D cross sections perpendicular to the colon midline is also described in U.S. Pat. No. 5,458,111, issued Oct. 17, 1995 to Coin. However, direct interpretation of the cross-sectional images is difficult because a scan of the colon consists of several hundred axial tomograms. Without advanced image manipulation tools, interpretation of the colon's complex three dimensional shape from these cross sections alone is very difficult for a medical practitioner.
One approach to improve accuracy involves production of reformatted 2D images at cross sections and orthogonal angles to the colon midline. These reformatted 2D images can provide complimentary diagnostic information when viewed with corresponding intraluminal 3D images. Exam efficiency can be improved with innovative 3D rendering techniques that allow fast, interactive evaluation on low priced computer hardware.
Therefore, there is a need for new techniques which provide efficient and accurate evaluation of the colon using helical CT data. There is a need for displaying coronal, sagittal, and axial views of the colon. There is also a need for displaying a three dimensional image of the colon. There is a further need for displaying an unfolded or open view of the colon.